Recent advances in medical science and biological engineering have made a meniscus prosthesis more practical. A desirable form of meniscus prosthesis is shown in U.S. Pat. No. 4,344,193 (the disclosure of which is hereby incorporated by reference herein). While the device illustrated in that patent has many practical advantages, it has not yet been extensively utilized in actual human knees.
According to the present invention a device--and a method of implantation thereof--are provided that have the same advantages of the meniscus prosthesis disclosed in the U.S. Pat. No. 4,344,193 , and additionally have other advantages. In addition to the advantages contained in the patent, the prosthesis according to the invention stabilizes the knee joint against unphysiological motions or deviations. It especially provides for stabilization in conjunction with ligamentous reconstructions. Further, and perhaps most significantly, the prosthetic device according to the invention translates compression and torsional loads into tensile or "hoop" stresses in the prosthesis.
The prosthetic device according to the invention has two major components, a body, and a tail means. The body is very similar to the body in the 4,344,193 patent only without the raised prominences. The body is of biocompatible, deformable, flexible and resilient material such as silicone rubber, or a number of natural materials (e.g. collagen, tendon or fibrocartilage). It has an arcuate construction, of significantly less than 360.degree. but at least about 150.degree.. The cross-sectional area of the radial exterior is greater than the cross-sectional area of the radial interior; that is the body has a shape, when implanted, of a naturally occurring meniscus. The body bears the compressive loads of the femoral condyle against the tibia, translates those loads to the tail means as tensile stresses, stabilizes the femoral condyle on the tibia, lubricates and aids in the metabolism of the articular surfaces of the joint, and expands and presses against the soft tissues around the joint. It also may serve as an attachment of the prosthesis to the soft tissues surrounding the joint.
The tail means may have a variety of constructions. Preferably the tail means provide a continuous loop, either being formed as an integral loop originally with the body, or being connected to the ends of the body and ultimately being attachable together at free ends thereof, or being connected at one end of the body and being attachable at the free end thereof to the other end of the body. The tail means provides a continuous loop circuit for the the propagation of tensile (hoop) stresses, provides soft tissue anchorage for stability (particularly against unphysiological motions or deviations), and provides proprioceptive feedback. Proprioceptive feedback or "joint position sense", is an important physiological mechanism which assists in preventing injury. The tail means also may allow for expansion and gliding to conform to the torsional, translational, and compressive loading of the prosthesis. In use the tail means is not truly attached to the bone, although it is placed in operative association therewith. Motion between the tail means and the bone must be allowed so that the prosthesis may elongate and shorten as tension is developed within it by compressive loading of the knee.
The tail means typically will be disposed in an aperture in surrounding bone, such as a bony trough, through-extending bore, channel, or the like. In some circumstances it is desirable to have a sleeve surrounding a portion of the tail means that is disposed in operative association with the bone. The sleeve allows for gliding movement of the prosthesis with respect to the bone while still providing for "locking" or "anchoring" of the prosthesis with respect to the bone. A polyethylene tube may serve as a gliding sleeve, or the outer surface thereof may be coated with Dacron mesh or metal porous material to allow soft tissue or bony in-growth, respectively. The sleeve also may serve as a point for suture fixation.
The tail may be completely integral with the body, or may be formed of a separate material. In fact the body may be formed around a portion of the tail (which could be in the form of a hoop or strip). The tail has substantial thickness, on the order of at least 30% of the cross-sectional area of the body. This clearly distinguishes it from prior art prostheses which may have sutures extending therefrom, which sutures are thin and are not capable of performing the functions of the tail of the prosthesis according to the invention. It is desirable that the tail have a smaller cross-sectional area than the body, but it may have a cross-sectional area 100% that of the body.
The invention also comprises a method of implanting a meniscus prosthetic device in a human knee, the prosthetic device having an arcuate body of biocompatible, deformable, flexible, and resilient material, and a tail for stabilizing the body. The method comprises the steps of: (a) Inserting the body into position in the knee to take the place of a naturally occurring meniscus between one femoral condyle and the corresponding tibia. (b) Placing the tail into contact with bone associated with the knee so that the tail will stabilize the body in the knee against unphysiologic motions or deviations, yet allowing movement of the body to achieve constant conformation to the femoral condyle and tibia under torsional, translational, and compressive loading. And (c), attaching the device to soft tissue surrounding the knee joint.
The device--as described above--used in the method according to the invention preferably comprises a tail integral with the body and comprising a continuous uninterrupted extension of the body, defining a closed loop, and a trough is either formed or naturally existing in the bone surrounding the knee joint. In such situations, step (a) is practiced by distracting the femoral condyle and tibial surfaces, and passing the device between them, and step (b) is practiced by placing the tail in the bony trough. The trough may be in a central portion of the bone, or around the periphery of the bone.
Where the body has first and second ends with the first tail member extending integrally from the first end and a second tail member extending integrally from the second end, with the tail members having free ends, then step (b) is practiced by passing the tail members into operative association with openings in bone (e.g. drilled through-extending openings) surrounding the knee joint, and then affixing the free ends of the tail members together. Alternatively, the tail members could be passed through sleeves, and knotted at the free ends thereof to prevent passage through the openings.
It is the primary object of the present invention to provide a useful and effective meniscus prosthesis, and method of implantation thereof. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.